1. Field of the Invention
The present invention relates to an optical functioning glass, an optical fiber, an optical waveguide device, and an optically active apparatus used for optical amplification and the like at the 1.3-.mu.m wavelength band.
2. Related Background Art
Efforts have been made to manufacture optical devices such as a fiber amplifier, a fiber sensor, and a fiber laser by using a glass doped with a rare-earth element for the application in the fields of optical communications at the 1.3-.mu.m wavelength band and the like. For example, a report has been made (ELECTRONICS LETTERS, 1990, Vol. 26, No. 2, pp. 121-122) in which a neodymium ion (Nd.sup.3+) was added to phosphate-based multi-component glass, an optical fiber was formed from this glass, and laser oscillation characteristics of this optical fiber were evaluated. This report shows the characteristics of the optical fiber that a fluorescence peak wavelength was 1.32-.mu.m, an ESA (excited state absorption) peak wavelength was 1.31-.mu.m, and an oscillation peak wavelength was 1.36-.mu.m.
In the multi-component glass indicated in the above report, a sufficiently high laser gain cannot be obtained at the 1.3-.mu.m wavelength band, because the intensity of the fluorescence peak of Nd.sup.3+ at the 1.32-.mu.m wavelength is relatively weak, and because a relatively high absorption peak caused by ESA transition is present at the wavelength of 1.31-.mu.m.
Further, when optical amplification is performed by utilizing induced or stimulated emission as in the above optical fiber, problems are not only that the fluorescence peak at 1.31-.mu.m wavelength is weak but also that other fluorescence peaks due to possible transition are present. More specifically, in the above optical fiber, in addition to the fact that the fluorescence peak of Nd.sup.3+ at the 1.3-.mu.m wavelength band is relatively weak, the fact that emissions of Nd.sup.3+ at the 0.8- and 1.06-.mu.m wavelength bands corresponding to other possible transition is relatively strong poses a problem. Due to the induced emission by the light emissions at the 0.8-.mu.m and the 1.06-.mu.m wavelength band, the stimulated emission at the 1.3-.mu.m wavelength band is impeded, and an induced emission efficiency is significantly reduced.